1. Field
The present invention pertains to a medical device delivery catheter system. A delivery catheter system is typically used to deliver devices such as stents, stent-grafts, grafts, or other diagnostic or therapeutic devices.
2. Discussion of Related Art
It is desirable in various situations to access a vessel, a constricted vessel portion for purposes such as maintaining an open passageway through a vessel portion. Such situations arise, for example, in conjunction with arteriosclerosis that restricts or stops blood flow through a vessel. In many procedures, a guiding catheter is percutaneously introduced into a patient's vessel. For instance, a guide catheter is introduced into the patient's cardiovascular system into a coronary artery in a typical percutaneous transluminal coronary angioplasty procedure. Often, a guidewire is used in conjunction with fluoroscopy to advance the catheter into the vessel. Procedures that utilize such a guide catheter include opening an artery, preventing arterial closure, and implanting a prosthesis, stent, stent-graft, graft, or other device to maintain vascular patency. In many procedures, a guide catheter helps delivering the particular device (e.g., a stent) to a treatment site and needs to be withdrawn after the device is delivered. Moreover, in certain applications, the guide catheter also functions as a delivery catheter or a housing for a delivery catheter for the device. Withdrawing the guide catheter or the delivery catheter is often a challenging task as illustrated in FIGS. 1-3.
To help prevent arterial closure, repair dissection, or prevent restenosis following dilatation, a physician can implant an intravascular prosthesis, or a stent or other device such as a stent-graft, or a graft, for maintaining vascular patency inside the artery at the lesion. There are typically two types of stents, a self-expanding stent and a balloon expandable stent. The balloon expandable stent is delivered on a balloon and the balloon is used to expand the stent. The self-expanding stent may be made of shape memory materials such as Nitinol (NiTi) or constructed of regular metals but of a configuration that allows self-expansion. The stents can also be made of polymeric materials.
Stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel or other anatomical lumen. Stents have been used for many treatment procedures. For instance, stents have been used to maintain vascular patency, open up an obstructed artery, repair aneurysms, repair dissections, support artificial vessels, and support other lumens in a patient's body.
FIG. 1 illustrates an example of a conventional catheter delivery system 100 for a self-expanding stent. In one example, a stent 102 is placed within a retractable sheath 108 in a compressed, collapsed, or undeployed state. The stent 102 is placed between an inner member 104 and the sheath 108, which could be a catheter. If there is a balloon to deploy the stent 102 (if the stent 102 is not self-expandable), the balloon (not shown) is placed under the stent 102 and outside the inner member 104. The inner member 104 may be configured to accept a guidewire 112 to help maneuver the stent delivery system 100 to a treatment site. The stent 102 and the inner member 104 are placed within an outer member 106. In conventional delivery methods, to deliver the stent 102, the retractable sheath 108 is pulled back proximally to expose the stent 102 and to allow the stent 102 to deploy as shown in FIG. 2 while the inner member 104 remains in place. In some cases, the sheath 108 is bonded to the outer member 106 and withdrawing the outer member 106 also retracts the sheath 108 to deploy the stent 102. In another example, a pullback wire (not shown) is included. The pullback wire is attached to the sheath 108 such that one can pull on the pullback wire to independently withdraw the sheath 108 in order to deploy the stent 102. A handle (not shown) with a pullback mechanism is provided at the proximal end of the delivery catheter system 100 to retract the sheath 108. In one example, a stopper 110 is provided to prevent the stent 102 from sliding proximally while the sheath 108 is being withdrawn. After the stent 102 is deployed, the catheter assembly is removed.
Delivery systems such as those described work well in relatively simple vascular anatomies. However, such systems do not always provide a smooth withdrawal of the sheath 108 in a situation where the delivery systems have to go through tortuous pathways, such as those seen in the anatomy of the coronary arteries. The tortuous pathways often cause buckling or kinking of the inner member 104, outer member and catheter assembly during sheath retraction and increase contact areas 120 as well as frictional forces between the fixed inner member 104 and the sliding outer member 106 and the sheath 108 as illustrated in FIG. 3. For instance, the inner member 104 starts to lock on the outer member 106 due to crimping, kinking, friction, or buckling of the inner member 104 that is caused by a tortuous pathway. Thus, during an interventional process, it may be difficult to withdraw the sheath 108 or other components of the delivery system and in extreme cases, the stent 102 may be undesirably moved or withdrawn. Some delivery systems also provide a separate lumen for a pullback wire that is used to retract the sheath 108. These delivery systems suffer the same problem caused by the buckling or kinking of the delivery systems due to the tortuous pathways. The forces between the fixed inner member 104 and the sliding outer member 106 and/or the sheath 108 can become so large that the delivery system locks and prevents sheath retraction and potentially, stent deployment.
In some cases, to prevent the buckling problem, the inner member 104 needs to be stiff to prevent buckling or kinking during the sheath retraction process. However, having a stiff component in the delivery system is not desirable especially when the delivery system needs to go through tortuous pathways. Furthermore, with a requirement that all the components in a delivery system be as small in dimension as possible for various vasculature pathways, the outer member 106 and the inner member 104 have very similar diameter dimensions making the buckling or kinking problem even more pronounced. Accordingly, there is a need for a system that accomplishes the delivery of a medical device within vasculature while addressing the shortcomings found in conventional devices. The present invention satisfies these and other needs.